To promote efficiency and productivity in a silk screening process, a need exists for a silk screen frame that is easily assembled, tensioned, re-tensioned and disassembled. Prior art devices have usually attempted to conform to one or more of the above criteria, but have, in the process, become less desirable in other criteria. For example, Messerschmitt, U.S. Pat. No. 3,211,089, attempts to provide a frame and screen which will assure even tension across the surface of the screen. However, in so doing, the frame is complex and is not easily assembled and disassembled and the screen requires separate preparation to affix a plastic border. Similarly, deGroot, U.S. Pat. No. 3,230,872, discloses a method which focuses on securing the screen within a groove and on tensioning the screen at the expense of complexity; which makes assembly, disassembly and re-tensioning more difficult and time consuming.
Hughes, U.S. Pat. No. 3,485,165, provides a silk screen frame which allows for uniformity in tensioning a screen and rigidity to retain the proper tension, but it does so using a complex mechanical adjustment system. Lamb, U.S. Pat. No. 4,144,660, is likewise concerned with adjustability which would aid in tensioning and re-tensioning, but again, it adds complexity to the design resulting in the need for special tools and making assembly and disassembly difficult.
Attempts to simplify frame construction which would aid assembly and disassembly have, in prior art devices, resulted in subsequent losses in the ease of tensioning and re-tensioning For example, Johnson, U.S. Pat. No. 3,625,274, is a less complex frame than the previously discussed prior art devices, but makes adjustment in one dimension impossible because the entire corner is expanded with one adjustment screw. Also the frame fit together with a "tight frictional fit" which only complicates assembly and disassembly. The greatest level of simplicity is engendered by Bubley, U.S. Pat. No. 4,452,138. This device uses friction and a bonding agent to make the frame rigid. Assembly is simple; however, the presence of the bonding agent makes re-tensioning and disassembly impossible once a bond has set.
The present device provides a mesh frame which meets the previously listed criteria without unnecessary complexity. The present device, has a selective locking mechanism which provides excess tolerance between the frame rails and corner-pieces so that assembly and disassembly are easy. Once a screen is in place, however, the frame rails are rotated by the tension placed on them by the mesh and engage the selective locking mechanism. As tension is increased by eight independent adjustments, the lock becomes more solid and the tolerance between the frame rail and corner piece is reduced to zero.
With eight independent adjustments the present device allows for proper uniform tensioning of the screen and the placement of the adjustment screws allows re-tensioning of the screen without removal from a silk screen press.
The same excess tolerance that makes assembly easy is reintroduced to the frame by removing the tension from the screen. Once the tension is removed the frame rails may be rotated away from the locked position and there is once again excess tolerance in the frame which allows for the breaking of dried ink "welds" and ease of disassembly.
In this way, the present device overcomes the limitations of the prior art devices which makes for a more productive and efficient silk screen frame.